Within the Third Generation Partnership Project (3GPP), specifications for telecommunication systems are proposed and decided upon. One such telecommunication system is called Long Term Evolution (LTE).
According to LTE, Orthogonal Frequency Division Multiplexing (OFDM) is used for transmission in downlink and Discrete Fourier Transform (DFT)-spread OFDM is used for transmission in uplink. Downlink refers to transmission from a so called eNB to a user equipment. Uplink refers to transmission from the user equipment to the eNB.
An LTE downlink physical resource, often referred to as a resource element, has a certain extension in time and frequency domains. In the frequency domain, the resource element extends over, or corresponds to, one so called OFDM subcarrier. In the time domain, the resource element, extends over, or corresponds to, one so called OFDM symbol interval.
In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, where each radio frame consists of ten equally-sized subframes. Each subframe has a length of 1 ms.
Furthermore, allocation of the resource elements in LTE is performed while organizing the resource elements into Resource Blocks (RB). A resource block corresponds to one slot, 0.5 ms, in the time domain and 12 contiguous subcarriers in the frequency domain. Each subcarrier is 15 kHz wide. A pair of two adjacent resource blocks in the time domain, 1.0 ms, is known as a resource block pair. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the transmission bandwidth.
The notion of Virtual Resource Blocks (VRB) and Physical Resource Blocks (PRB) has been introduced in LTE. The actual resource allocation to a user equipment is made in terms of VRB pairs. There are two types of resource allocations, localized and distributed. In the localized resource allocation, a VRB pair is directly mapped to a PRB pair, hence two consecutive and localized VRB are also placed as consecutive PRBs in the frequency domain. On the other hand, the distributed VRBs are not mapped to consecutive PRBs in the frequency domain; thereby providing frequency diversity for data channel transmitted using these distributed VRBs.
In order to efficiently and dynamically use radio spectrum, LTE supports flexible allocation of transmission bandwidths. The pre-determined transmission bandwidths are: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. Therefore, in order to fulfill LTE specifications, any user equipment, fulfilling the LTE specifications, must support all of the aforementioned transmission bandwidths.
In LTE there are reference signals, which are sequences consisting of sequence elements, each of which associated with a sequence element number. The sequence elements are mapped to sub-carriers that are distributed with regular or irregular pattern over bandwidth.
In the following description, resource blocks and sequence elements are denoted as examples of enumerable elements.
A known LTE system comprises a radio base station, such as an eNB. A user equipment is located in a cell served by the radio base station. When the user equipment attempts to access a carrier of the radio base station, the user equipment receives various signalling about the carrier from the radio base station. At least some of the signalling is received on a broadcast channel, which is common to all of the pre-determined transmission bandwidths. The signalling informs the user equipment of the transmission bandwidth of the carrier. Accordingly, the user equipment selects to use a transmission bandwidth that matches the transmission bandwidth of the carrier.
A disadvantage, in connection with the above mentioned transmission bandwidth selection process of the LTE system, is that the number of available bandwidths is limited to a number of pre-determined bandwidths. As a consequence, only a user equipment with a transmission bandwidth that exactly matches the bandwidth of the carrier is able to access, e.g. able to camp on it, the radio base station.